 Peter Flanagan played in Hull Kingston Rovers' 5-13 defeat by Widnes in the 1963–64 Challenge Cup Final during the 1963–64 season at Wembley Stadium, London on Saturday 9 May 1964, in front of a crowd of 84,488.Peter Flanagan played in Hull Kingston Rovers' 25-12 victory over Featherstone Rovers in the 1966 Yorkshire County Cup Final during the 1966–67 season at Headingley Rugby Stadium, Leeds on Saturday 15 October 1966, played in the 8-7 victory over Hull F.C.in the 1967 Yorkshire County Cup Final during the 1967–68 season at Headingley Rugby Stadium, Leeds on Saturday 14 October 1967, and played in the 11-7 victory over Castleford in the 1971 Yorkshire County Cup Final during the 1971–72 season at Belle Vue, Wakefield on Saturday 21 August 1971.